diff --git a/utils/analytics.py b/utils/analytics.py
index 848aee7..db9a170 100644
--- a/utils/analytics.py
+++ b/utils/analytics.py
@@ -101,6 +101,20 @@ def get_or_create_analytics_session():
             # PWA detection from cookie (set by JS in standalone mode)
             pwa_cookie = request.cookies.get('pwa_mode') == '1'
             pwa_display = request.cookies.get('pwa_display', '')
+            # DEBUG: log all cookies for mobile sessions to /tmp/pwa_debug.log
+            if user_session.device_type == 'mobile':
+                try:
+                    with open('/tmp/pwa_debug.log', 'a') as _f:
+                        import json as _json
+                        _f.write(_json.dumps({
+                            'session_id': user_session.id,
+                            'path': request.path,
+                            'pwa_mode': request.cookies.get('pwa_mode'),
+                            'pwa_display': request.cookies.get('pwa_display'),
+                            'all_cookies': list(request.cookies.keys()),
+                        }) + '\n')
+                except Exception:
+                    pass
             if not user_session.is_pwa and pwa_cookie:
                 user_session.is_pwa = True
             db.commit()